[lust4speed]

This one has me confused, and I'll get to the punch line first by telling you that I solved the problem by installing an old stock 8-bolt water pump that I had on the shelf.

This is a new engine build of a 1966 GTO 389. Owner purchased and I installed a new Flowkooler cast iron water pump with the blue aluminum impeller. Had a mild rattling coming from the water pump on start up. Sounded at first like the two plates were vibrating and causing the racket so I took the water pump back off and confirmed that the plates were properly clearanced, and then added some Ultra Grey between the plates and between back plate and housing to absorb any vibrations. Put the assembly back together and got around to starting the engine on the run stand three days later so Ultra Grey was nicely set up. There was still the same vibration and I convinced myself that it might be the '66 two piece water pump pulley that might have the two pieces loose from each other so I dug through the pile and found a matching pulley, and that one didn't help. Final straw was taking things back apart and checking everything again and then installing with a '67 pulley, and that didn't change anything. Pulled pump back out and it looks perfect and spins smoothly by hand. Put everything back together and fired up the engine without coolant and no vibration or rattling. Thought I solved things until added coolant and the same rattling returned. So it is quiet with no water and vibration with water .

Pulled the pump off again and substituted out a used bone stock pump I had on the shelf. No other changes and the rattling was gone and dead smooth anywhere in the RPM band.

Anyone ever have a remotely similar problem with the Flowkooler pump? I thought it was going to be a bad bearing until the pump ran dead smooth without any coolant in the system. If it had been a bearing I would think the vibration would have been worse.

No witness marks on either the plates or the anodized impeller.

[chuckies76ta]

Morning Mike. Check the balancer bolts that hold the pulley or pulleys. I have seen several issues on engines with these loosing up without blue locktite. I would get yourself a factory pump with the cast impeller. There the best in my opinion.

[steve25]

Looks to me like the center of the impeller ripped out.

With fluid in the motor for it to move around the force of rotation just kept it shifted to one side, but once having to move fluid it would rattle around on that failed center section as fluid made its way in and out of the pump.

[72projectbird]

Just a guess, but the coolant/water is putting a load on the bearings that otherwise isn't there when the system empty? Or maybe it's creating a nasty case of cavitation?

[JSchmitz]

Cavitation causes a rattling sound. Any restriction on the suction side of the pump? Air trapped somewhere?

[lust4speed]

Engine is on the engine break-in stand so no thermostat and the aluminum radiator has been used for dozens of runs since I replaced the failed brass one a couple years ago. Engine is a fresh build and will be going to Westech on Wednesday. At the moment I'm just glad that the stock pump solved the problem since there is a two month backlog to get in and I would have been the bad guy if I had to cancel the appointment.

Don't think I mentioned it before but there wasn't a sound when breaking in the engine between 1,800-2,200 RPM, but when the break-in was done and I kicked the RPM up to 3,000+ to set max timing the pump sounded like it was going to rattle apart. Anything under say 2,600 RPM and it's quiet. 100% repeatable with the RPM increase.

First thing I did was remove the belt and rap the engine up and no noise. Then replaced the two-piece water pump pulley with a solid pulley and that didn't help. Then reset the plates twice with the last time applying Ultra Grey as a dampener medium behind the rear plate and between the plates so it would keep the rear plate from moving and/or vibrating. Even with the Ultra Grey set up the intensity of the rattling didn't decrease. Substituting out the pump for a used stock one did make the problem go away. The plates were nicely glued in place so I didn't have to touch them on the pump substitution.

When I removed the Flowkooler and put on a standard pump the vibration noise totally went away so definitely related to the Flowkooler. The idea that one of the bearings inside the Flowkooler might be causing the problem sounds like a strong possibility. It's either that or some strange interaction between the new impeller design and the flat on the impeller reacting with the plate(s) causing cavitation.